As is known, in balancing machines, the rotating body, and in particular the wheel of a motor vehicle, is fitted on one end of a shaft which is turned and is supported by a frame provided with force transducers adapted to measure the centrifugal force generated by the imbalances present on the rotating body.
The frame that supports the shaft is fixed generally to the base of the machine by way of relatively elastic systems, which are capable of providing degrees of freedom to the movement of such frame. The degrees of freedom are locked by force transducers.
In this manner, it is possible to obtain from the transducers a signal which corresponds to the forces which are induced by the imbalance present on the motor vehicle wheel and are discharged onto the basic structure of the balancing machine.
The rotating body is turned at the speed needed for measurement by using electric motors connected to the shaft by means of belts and pulleys or a motor which is mounted in axial alignment with the rotating body.
The system with motor and belt drive is considered convenient, since the drive allows to reduce the selected rotation rate for the proper operation of the balancing machine.
Measurement of the imbalance in fact can be obtained correctly from a speed on the order of 80-100 rpm of the rotating body, while a normal electric motor has a much higher speed.
By means of the reduction that can be obtained from the belt, it is possible to use a motor of limited power which is therefore less expensive.
However, the solution described above suffers the drawback that the vibration generated by the rotating belt or by the eccentricity of the driving pulley affects negatively the measurement of the imbalance forces.
Solutions are known in which the transducers have measurement axes which are substantially parallel to each other and contrast the movement of the frame suspended on relatively flexible springs.
This shape of the frame of the balancing machine allows to mount the motor so that it is laterally adjacent to the frame or mounted on board the frame. This embodiment with transducers having parallel axes, however, suffers drawbacks due to complexity and construction and to the difficulty in obtaining from the transducers signals which can be correlated easily to the forces generated by the imbalances.
Therefore, also the above described solution suffers drawbacks.